leetcode — subsets-ii

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Source : https://oj.leetcode.com/problems/subsets-ii/
 *
 *
 * Given a collection of integers that might contain duplicates, S, return all possible subsets.
 *
 * Note:
 *
 * Elements in a subset must be in non-descending order.
 * The solution set must not contain duplicate subsets.
 *
 * For example,
 * If S = [1,2,2], a solution is:
 *
 * [
 *   [2],
 *   [1],
 *   [1,2,2],
 *   [2,2],
 *   [1,2],
 *   []
 * ]
 *
 */
public class SubSet2 {

    private List<List<Integer>> result = null;

    /**
     *
     *
     * @return
     */
    public List<List<Integer>> subset (int[] arr) {
        result = new ArrayList<List<Integer>>();
        List<Integer> set = new ArrayList<Integer>();
        Arrays.sort(arr);
        recursion(arr, 0, set);
        return result;
    }

    private void recursion (int[] arr, int index, List<Integer> set) {
        if (index == arr.length) {
            return;
        }
        // 初始化上一次出栈的元素为当前将要进栈的元素-1，为了不和将要进栈的元素相同
        int last = arr[index]-1;
        for (int i = index; i < arr.length; i++) {
            // 如果上一次出栈的元素等于准备进栈的元素，则说明两个元素一样，跳过
            if (last == arr[i]) {
                continue;
            }
            set.add(arr[i]);
            List<Integer> temp = new ArrayList<Integer>(set);
            result.add(temp);
            recursion(arr, i + 1, set);
            last = set.remove(set.size()-1);
        }
    }

    private static void print (List<List<Integer>> list) {
        for (List<Integer> arr : list) {
            System.out.println(Arrays.toString(arr.toArray(new Integer[arr.size()])));
        }
        System.out.println();
    }

    public static void main(String[] args) {
        SubSet2 subSet2 = new SubSet2();
        int[] arr = new int[]{1,2,2};
        int[] arr1 = new int[]{1,2,3,3,3,3,4};
        print(subSet2.subset(arr));
        print(subSet2.subset(arr1));

    }
}